The present invention relates to a control system for an internal combustion engine, and more particularly to a control system for an internal combustion engine mounted on a vehicle including a pressure regulator for regulating the pressure of fuel to be supplied to the internal combustion engine on the basis of the pressure in a fuel tank.
A known fuel supply control system, disclosed in Japanese Patent Laid-open No. Hei 7-166919, is configured such that a fuel pump and a pressure regulator are provided in a fuel tank. In this control system, the fuel pressure is regulated on the basis of the pressure in the fuel tank and then the pressure-regulated fuel is supplied to an internal combustion engine via a fuel injection valve. According to this control system, the fuel pressure is controlled by the pressure regulator so that a pressure difference between the fuel pressure and the pressure in the fuel tank is kept at a constant value, and the valve opening period of the fuel injection valve is corrected according to the pressure in the fuel tank and the pressure in the intake pipe of the engine. Such correction of the fuel pressure and the valve opening period of the fuel injection valve is employed because the amount of the fuel to be injected in the intake pipe of the internal combustion engine via the fuel injection valve changes depending on the fuel pressure and the pressure in the intake pipe even if the valve opening period of the fuel injection valve is kept constant, and the fuel pressure changes along with a change in pressure in the fuel tank.
When the pressure in the fuel tank changes, however, there is a time lag until the change in pressure in the fuel tank actually exerts an effect on the fuel injection amount. Such a time lag changes depending on the required fuel amount of the engine, that is, the amount of fuel to be supplied to the engine. As a result, the correction of the valve opening period of the fuel injection valve according to the pressure in the fuel tank and the pressure in the intake pipe is insufficient. Therefore, it has been expected to further improve the accuracy of the fuel injection amount control.
An object of the present invention is to provide a control system for an internal combustion engine, which can more accurately control the amount of fuel to be injected by the fuel injection valve, when regulating the fuel pressure on the basis of the pressure in the fuel tank.
To achieve the above object, there is provided a control system for an internal combustion engine, including at least one fuel injection valve, fuel injection amount control means, fuel pressure control means, fuel tank pressure detecting means, intake pipe pressure detecting means, first correcting means, required fuel amount calculating means, and second correcting means. The at least one fuel injection valve injects fuel supplied from a fuel tank into an intake pipe of the engine. The fuel injection amount control means controls the fuel injection amount by controlling the valve opening period of the at least one fuel injection valve. The fuel pressure control means is provided in the fuel tank and controls the pressure difference between the pressure of fuel to be supplied to the at least one fuel injection valve and the pressure in the fuel tank such that the pressure difference is at a constant value. The fuel tank pressure detecting means detects the pressure in the fuel tank and the intake pipe pressure detecting means detects the pressure in the intake pipe. The first correcting means calculates a correction amount as a function of the pressure in the fuel tank and the pressure in the intake pipe, and corrects the valve opening period of the at least one fuel injection valve as a function of the calculated correction amount. The required fuel amount calculating means calculates a required amount of fuel to be supplied to the engine as a function of an operating condition of the engine. The second correcting means corrects a change rate of the correction amount calculated by the first correcting means, according to the required fuel amount.
With this configuration, the valve opening period of the fuel injection valve is corrected according to both the pressure in the fuel tank and the pressure in the intake pipe, and the change rate of the correction amount of the valve opening period is corrected according to the required amount of fuel to be supplied to the engine. As the required fuel amount (which is the amount of fuel to be injected by one opening of the fuel injection valve) becomes large, a time lag until the change in pressure in the fuel tank actually exerts an effect on the fuel injection amount becomes long. Accordingly, the amount of a fuel to be injected by the fuel injection valve can be accurately controlled by reducing the change rate of the correction amount calculated according to the pressure in the fuel tank.
The first correcting means preferably corrects the valve opening period of the fuel injection valve so that the valve opening period becomes longer as the pressure in the intake pipe becomes higher.
The first correcting means preferably corrects the valve opening period of the fuel injection valve so that the valve opening period becomes shorter as the pressure in the fuel tank becomes higher.
The second correcting means preferably corrects the change rate of the correction amount of the valve opening period so that the change rate decreases as the required fuel amount increases.
The control system preferably further includes pressure reducing means for reducing the pressure in the fuel tank to a value which is lower than the atmospheric pressure during operation and stoppage of the engine.
When the control system includes the pressure reducing means, the above-described effect of the present invention may be more positive, since a change in pressure in the fuel tank is large.
The second correcting means may correct the change rate of the correction amount calculated by the first correcting means, according to a non-corrected value of the valve opening period of the at least one fuel injection valve, instead of correcting the change rate of the correction amount according to the required fuel amount.